Method of making dental impressions



March 11, 1969 v, KUBALEK 3,431,648

METHOD OF MAKING DENTAL IMPRESSIONS Filed July 28, 1967 FlOInCe clKubcllek Execuhq'x of Es+o+e 02 Milo \[Kubalek Deceased United States Patent 2 Claims ABSTRACT OF THE DISCLOSURE The method of making a dental impression involving the sequential steps of (a) formulating a liquid chemically setting material into an essentially liquid consistency; (b) lodging a quantity of said material in a tray and applying said impression material face to face with an oral surface area to be reproduced; (c) reducing the air pressure to a predetermined subatmospheric level in said tray by withdrawing air from between the interfaces of the area to be reproduced and the surface of the impression material; and (d) maintaining said material in contact with said area until the impression material is chemically set at the attained subatmospheric pressure.

This invention is adapted to reproduce an intaglio likeness of the anatomic areas and surfaces of a patients mouth when taking an impression preparatory to fitting a denture therein. This is produced by creating a subatmospheric pressure between the adjacent surfaces of a liquid cementitious investment material and the tissue to be reproduced. A liquid that sets chemically can reproduce both soft and hard tissues with equal bearing surfaces and if the patient performs prescribed exercises while the impression material is still liquid, there will be reproduced in the opposed surface of the investment material a dynamic mirror image rather than a static one.

The impression thus made also provides an accurate means of checking the border and posterior palatal seals before making the final impression, and provides comfortable seals when the finished denture is made.

A search of the dental literature has failed to reveal the use of atmospheric pressure to hold the impression tray and its contained material in a completely undisturbed position while recording peripheral and bearing area anatomy.

Since the impression is the keystone of a successful denture, it becomes necessary to correct the shortcomings of previous techniques, such as instability, insecurity, encroachments on ligamentous and muscular space, displacement and compression of tissues beyond tolerable limits on one hand, and underloading of tissues, which should be utilized to equalize the support afforded by less capable supporting tissues, 0n the other.

When the natural teeth are lost, it becomes necessary to replace the dentition with a prosthetic appliance known as a full upper denture in the case of the maxillary structures, or a full lower denture in the case of the mandibular structures. Heretofore it has been the practice to take a preliminary impression of the ridges and the overlying mucosa with a modeling compound material, which was heated in water until plastic, and inserted into a metal tray which had been selected, to conform to the contours of the ridge and cover the area to be included in the impression without impinging on muscular or ligamentous attachments. The loaded tray was carried to the mouth and forced into place with digital pressure until the entire mass was chilled with water and removed. In earlier days, a tray was filled with a creamy mix of plaster and inserted in the mouth and forced into place until a certain consistency was reached, at which time the pressure was held constant until the plaster was assumed to be set. If inspection revealed obvious deficiencies, the entire impression was of necessity done over, since plaster allowed for no corrections. Inherently vague in depth and outline is the palatal seal area which resembles an upward swinging hinge. This area is examined with a large round instrument to ascertain how far it can be displaced upward. Wax is placed on the previously mentioned impression, the thickness of which the operator considers adequate to compensate for the displacement of the posterior palatal seal tissues. It was at this time that a procedure known as palatal relief was instigated. Palatal relief was a deliberate scraping and thus relieving of the impression over hard tissue areas, so that the resulting denture would not bear on these areas and cause soreness or instability. Since plaster does not lend itself readily to reinsertion in the mouth repeatedly, the operator could only resort to an inspection dictated by his experience as to whether the impression was suitable for use in the fabrication of a denture; Since no further checks were possible, it can be seen that results were at best conjectural. It was at this point in denture history that prosthetic men began to switch to a material known as modeling compound, which was mentioned earlier. Modeling compound was, as before stated, heated until plastic, placed into the tray and carried to the mouth, where it was held by finger pressure; until the operator chilled it with ice water and removed it from the mouth for inspection. Next, a system of heating the flanges of the impression with an alcohol torch until replasticized, replacing in the mouth, and holding by digital pressure, a procedure known as muscle trimming was instigated. Muscle trimming necessitated that the patient go through mouth opening and lip and cheek movements to create channels in the impression material, known as muscle trim. When the operator thought muscle trimming was adequate, the heated flange was chilled and the impression was removed from the mouth. This procedure was repeated in all quadrants of the compound impression until the operator was satisfied that all muscle markings were present. As in the case of the plaster impressions, the posterior palatal seal area was corrected with wax to a thickness assumed by the operator to be correct. Relief areas were scraped to relieve the hard areas.

Reviewing the foregoing comments, it is apparent that both maxillary and mandibular full and partial denture impressions were obtained by confining impression materials of varying consistencies in a tray which was inserted in the mouth and held with digital force in varying degrees in an attempt to adapt the impression material to the underlying mucosa.

The assumption was then made that if the anatomic form was recognizable and if the impression, upon reinsertion, appeared stable and had retention within acceptable limits, adequate adaptation and retention was obtained.

Basic techniques now in use are of the pressure and mucostatic varieties. Generally, pressure is applied either digitally in open mouth methods, or by the masticatory musculature in the functional or closed mouth methods. The mucostatic method requires that the tray be held digitally in a static position after initial seating.

Basic physiological principles dictate that no muscle, digital or masticatory, can sustain an unvarying pressure for the length of time required for any impression material to reach its final physical state, e.g., it can be re moved from the mouth without apparent distortion.

Most common faults incurred were inconsistent reproduction of the underlying tissues, conjectural estimates of periphery, and post dam morphology, re-

sulting in an impression of unknown accuracy, a peripheral seal of unknown quantity and a post dam of arbitrary depth and contour. In order to compensate for these hidden or obscure inadequacies, prosthodontists have resorted to palatal reliefs, over-extended peripheries and mechanically constructed posterior palatal seals.

In view of the foregoing facts, it would seem that further elaboration of these heretofore standard procedures is unproductive. While experience will minimize the imperfections and improve results, the basic inadequacies remain. Obviously, the situation calls for a form of seating and adapting pressure which is uniform in all directions, which permits controlled variation of the pressures required for a given case, and which eliminates the need for any manipulation whatsoever by the prosthodontist.

The methods and equipment hereinafter described will fulfill these requirements. They are perhaps 180 out of phase with present concepts in that atmospheric pressure is used to obtain reproduction of the mucosa underlying denture bases in the course of which other advantages will be shown to accrue.

Denture terminology has been augmented to described the new phenomena which have been observed and utilized.

The method and apparatus for practicing it will create an impression wherein the tray, impression material and tissues are all under inexorably unvarying pressure in all directions and controlled in degree by the prosthodontist to suit the requirements of the case. The tissues are, in effect, under subatmospheric pressure invested in the impression material under a controlled pressure norm for the case wherein every square millimeter of tissue must, in truth, share the load in equal proportion to its latent capability, both laterally and vertically.

Object To more accurately reproduce the anatomic form physiologically capable of accepting a denture base without compression and/or distortion of these tissues as they exist in their natural state. This must include the structures which make up the peripheral areas, as well as those which make up the bearing areas (the areas over which the denture base rests).

Old or existing methods The reproduction of the necessary anatomic form required for denture construction is called an impression. This is accomplished by confining an impression material of varying plastic as opposed to liquid consistency in a tray fitted to the patients alveolar anatomy. The tray, with its contained material, is seated and held in position with the fingers until the material has set.

Shortcomings (1) Pressure must be used to some extent and pressure on a yielding tissue will distort it.

(2) The tray must be held motionless to prevent distortion, which is impossible to do with any form of digital pressure.

(3) The peripheral areasmust be registered in the short time it takes the impression material to set without any means of determining the accuracy of what is registered.

(4) Any exercise used to muscle trim and record the periphery must be done with the fingers in the mouth. This is awkward and there is a good chance that there will be movement of the tray during these exercises. If this happens, a false recording will result.

The following is a summation of the faults of all prior denture impression technique collectively:

(1) Inadequate copy of tissues as they exist in function (dynamics) under a working denture due to faulty concepts, as follows:

(a) Use of materials, such as modeling compound which compresses or distorts tissues. Thus, the lateral aspects of tissue ridges and protuberances are obliterated and contorted so that they cannot serve lateral stabilizing influences. As these vertical tissue components try to recover their former height and angles under a denture, instability must result. In time the tissue suffers from sheer abuse and atrophy inasmuch as the vascular system is restricted.

(aa) Inability to copy infinitely minute detail.

(bb) Heating and reheating distortion.

(b) Fingers of operator in mouth restrict the most important muscle trimming and palatal seal requirements.

(aa) Impossible to maintain a steady pressure manually in even one direction or vector.

(c) Virtually impossible to obtain impression of post dam area morphology.

(d) No absolute method of verifying perfection of the impression.

(e) No method of maintaining immobility while arbitrarily doctoring the impression to make it usable.

The invention is hereinafter described with relation to the accompanying drawings, in which:

FIG. 1 is a plan view of a tray with which the invention may be practiced, and

FIG. 2 is a cross sectional view taken on the line 22 in FIG. 1, but upon an enlarged scale.

New method and apparatus The preliminary impression is taken in liquid alginate with a tray that will not displace or compress any of the tissue areas to be included in the final impression. The impression must include and reproduce as accurately as possible, the anatomic form necessary for the fabrication of an accurately fitting impression tray. The tray preferably is made of clear acrylic resin, the thickness of two sheets of pink base plate wax. A reinforcing rim is constructed from second molar to second molar to provide strength and to give bulk for the attachment of the special instruments used in this technique.

This tray is trimmed so that the peripheral borders are 2 mm. short of the muco-buccal and libial folds, sublingual fold space and the frenular areas are relieved to allow unimpeded function of these fibers. The object of this is to otbain a true functional or dynamic reproduction of these peripheral areas without interference by the tray.

The tray 1 is drilled and tapped in three places, 2, 3 and 4, respectively, to accommodate the threads of the special attachments, 5, 6 and 7, respectively. These holes are made in the reinforcing rim over the ridge in the central incisor and second molar areas, respectively. The attachments are threaded into position and connected with capillary tubing 8. All the connecting threaded areas are painted with a sealer (not shown). The tray is now connected to a pump provided with a gauge and valve assembly (not shown) that can indicate leakage by a raise in sub-atmospheric pressure. The tray attachments and all connections are checked for leakage. Then the proximate areas between the denture material and tissue to be reproduced are subjected to sub-atmospheric pressure by a pump with an evacuation action.

Determination of the peripheral and post dam Knowing now that the tray and its attachments are sealed, a prosthodontist is now ready functionally to copy the peripheral areas. For this purpose there is selected a material that will flow and mold as a liquid at body temperature, and then after a short period of time will become firm. This gives the prosthodontist full control over the peripheral recording material. When there is a deficiency we may add, and when there is an excess we may remove. Adaptol is added to the peripheral borders of the upper tray and to the post dam area. The Adaptol is warmed in a water bath at F. long enough to allow for complete softening. The tray with its peripheral recording material thoroughly softened is seated in the mouth and established there by atmospheric pressure, under 510" of vacuum. The patient now is instructed to do prescribed exercises which will allow the softened Adaptol to seek out and record the true peripheral and post dam morphology of the patient. After the patient has coinpleted the exercises, the Adaptol is chilled thoroughly with ice water and the tray is removed.

Preliminary impression The preliminary impression may be taken with any material that will flow as a liquid, adequately to reproduce dynamically the anatomic form necessary for the fabrication of an accurately fitting impression tray. In the maxillary arch this must include the labial and buccal frenums, any auxiliary frenuli, the muco-buccal fold areas, the hamular notch areas, the soft palate posterior to and including the fovea palatina, and the tissues of the hard palate and alveolar ridges.

The mandibular impression must show the retromolar pads, the external oblique lines, labial and buccal frenums, auxiliary frenuli, muco-buccal and muco-labial folds, sublingual fold space, mylo-hyloid line, and the ostiae of Whartons ducts.

After the preliminary impressions have been carefully scrutinized, they should be poured in stone within three to five minutes.

The invention produces the following new results:

(a) Provide the seating pressure desired.

(b) Furnish all necessary vectors of pressure to obtain an absolute dynamic copy of the tissues at work.

(c) Controllable pressure to suit the tissue.

(d) All pressures read on a gauge.

(e) All defects read on a gauge.

(f) Complete liberation of all involved musculature to mold peripheral anatomy because impression base is immobile.

(g) Provides for intimate contact of denture material and tissue never before obtained to the point where ploprioception is restored in many cases.

(h) Eliminates need for any reliefs whatsoever.

(i) Provides immobility of the dental bases.

(aa) Use of associated new equipment and instrumentation the relationship of the arches to each other in space can now be recorded with an accuracy previously unknown.

I claim:

1. The hereindescribed method which comprises taking a dental impression in a liquid chemical setting material in a tray to form an intaglio impression of the tissue to be reproduced, and then withdrawing air from the space between the tissue to be reproduced and the liquid chemical setting material to produce a subatmospheric pressure therein,

thereby to induce contact of said material upon said tissue under constant uniform induced pressure,

maintaining said pressure until said cementitious setting material attains a plastic condition to retain an inta glio reproduction of said tissue while holding said tray and said material by the difference in pressure between atmospheric pressure on the tray and the attained subatmospheric pressure adjacent the tissue being reproduced.

2. The method defined in claim 1 modified in that the yielding tissue being reproduced is subject to voluntary exercise while said subatmospheric pressure is being maintained'to produce a dynamic image rather than one of such tissue at rest.

References Cited UNITED STATES PATENTS 2,311,158 2/1943 Conway et a1. 3217 2,311,836 2/1943 Jones 32--17 2,312,171 2/1943 Jochum 3217 ROBERT PESHOCK, Primary Examiner. 

